The Dynamic Host Configuration Protocol (Dynamic Host Configuration Protocol, DHCP) is a dynamic address allocation solution based on the TCP/IP protocol. Compared with manual configuration of an IP address, the DHCP has advantages, for example, TCP/IP parameters (including an IP address, a subnet mask, a default gateway, a DNS, and the like) can be automatically configured, and an allocated IP address has a lease time and can be reclaimed for reuse after the lease time expires. In this way, all configuration information of the TCP/IP protocol may be stored on a DHCP server in a centralized manner. Centralized storage and management can prevent an IP address conflict, and can also free an administrator from burdensome manual configuration work. The advantages of the DHCP are becoming more prominent when a network scale at present is becoming larger.
Because the DHCP protocol needs to use a broadcast request to configure an IP address, this leads to a limitation that a DHCP client and the DHCP server need to be in a same physical network segment, where each physical network segment needs one DHCP server. If the DHCP client and the DHCP server are not in the same physical network segment, the DHCP client needs to use a DHCP relay agent (DHCP Relay Agent, DHCP relay agent) to acquire an IP address from the DHCP server that is in a different physical network segment. A network device with a DHCP relay function may receive a DHCP request packet and forward the DHCP request packet to a DHCP server in another physical network segment; in this case, the DHCP server can perform corresponding configuration for a DHCP client in a different physical network segment. Therefore, by using a DHCP relay agent, a limitation that each physical network segment needs one DHCP server may be lifted.
Currently, implementation of a DHCP relay agent is as follows: a DHCP client type is differentiated according to an OPTION60 or a MAC address in a DHCP request packet, and one DHCP gateway IP address is allocated to one DHCP client type. Therefore, an existing DHCP relay agent cannot be implemented in a case in which different network segments need to be allocated to a same client type, for example, two types of DHCP clients have a same OPTION60, but a DHCP server needs to allocate, according to their different area locations or different types of services provided by them, IP addresses in different network segments to the two types of DHCP clients.